As computers have become smaller and more numerous, the reasons for interconnecting them have grown more than in proportion. Remote computer networks like the Arpanet have been developed to promote resource sharing; for example the sharing of expensive specialized processors, software, and data bases. Multiprocessor computer configurations like the Illiac IV have been developed to get the increased performance of multiple computers working simultaneously on the same problem for either improved throughput or reliability. Local computer networks like that disclosed in U.S. Pat. No. 4,063,220, issued Dec. 13, 1977, entitled "Multi-Point Data Communication System With Collision Detection", have been developed for reasons resembling those of both remote computer networks and multiprocessors. The experimental communication system set forth in the patent, in particular, connects up to 256 communicating computers at 3 million bits per second through up to 1 kilometer of coaxial cable.
The aforementioned patent discloses apparatus for enabling communications between two or more data processing stations comprising a communication cable arranged in branched segments including taps distributed thereover. Tied to each tap is a transceiver which, on the other side, connects to an associated interface stage. Each transceiver includes, in addition to the usual transmitter and receiver sections, a gate which compares the data from the interface stage with the data on the cable and indicates whether such are equal. Should such be unequal, an interference between the transceiver and the cable is indicated, disabling the associated transmitter section. Each interface stage tied to such transceiver also includes an input and an output buffer on the other end thereof interfacing with a using device, such input and output buffers storing both the incoming and outgoing data. The output buffer is connected to a clock driven shift register which converts the buffered data to a serial stream, feeds such data to a phase encoder, which then connects to the transmitter or driver section of the transceiver. The input buffer is loaded by an input shift register which derives its clock from a phase decoder, the shift register and the phase decoder both connecting to the receiver section.
When the station is to start transmitting, the phase decoder detects the presence of other transmissions on the cable and detains the output shift register until no other transmissions are sensed. Once a transmission has begun, if interference is detected and the transmitter section is disabled, a random number generator is used to select an interval of time at the completion of which the next attempted transmission will take place. Concurrently, a counter counts the number of interferences, or collisions, which recur in the attempted transmissions of one data packet and weights the mean of the random number generator accordingly.
The input shift register is also connected to an address decoder which enables data transfer to the input buffer only during those times when the data is preceded by an appropriate address. Thus, the patent discloses a bit-serial receiver-transmitter network continuously connected to all communicating devices. More specifically, such is accomplished by forming a network of any one or plurality of transmitting media, such as coaxial cable, optical fiber or others, connected together into one branched network by constantly active devices, like repeaters, by which communications necessarily adapted to one medium are translated into the other medium.
According to the present invention, instead of electrically conducting coaxial cable, a fiber optic local computer network is disclosed. The present invention was first disclosed in an article entitled "Fibernet: Multimode Optical Fibers for Local Computer Networks" in the IEEE Transactions On Communications, Vol. COM-26, No. 7, July 1978, pp. 983 to 990.